Vacuum Cooling for the Food Industry

WEC Cooling is a UK based company operating from modern and extensive premises situated one hour away from Manchester and Liverpool International Airports. Our expertise in vacuum cooling is drawn from the construction and installation of vacuum coolers worldwide since the late 1980's. We operate through a network of agents and service companies as well as directly from our main factory.

Vacuum Cooling - What is it?

To the supermarket buyer or consumer it is a hallmark of quality to say that the product has been cooled by a unique process. Where vacuum cooling differs from conventional methods is that cooling is achieved from within the product rather than by trying to blow cold air over it.

It is the evaporation of water within the product that has the double effect of rapidly removing the field heat and sealing in the freshness. This is especially effective in reducing the browning effect on the butts of lettuce - no other process can offer you this marketing edge.

What are the applications?

As with most processes vacuum cooling cannot be applied to every type of products but those it is suited to are beyond reproach. In general, suitable products should be of a leafy nature or have a large surface to mass ratio.

Such products include:

  • Lettuce
  • Celery
  • Mushrooms
  • Flowers
  • Brocolli
  • Watercress
  • Beansprouts
  • Rolled turf
  • Babyleaf
  • Diced vegetables
  • Asparagus
  • Sweetcorn
  • Spring onions

What are the advantages?
Speed and efficiency are two features of vacuum cooling that are unsurpassed by any other method, especially when cooling pre-packed, boxed or palletised products. Assuming the product is not packaged in hermetically sealed packages the effect of bags, boxes or stacking density has virtually no effect on cooling times. For this reason it is common for vacuum cooling to be carried out on palletised product just prior to it being despatched. Cooling times in the order of 25 mins ensure that tight delivery schedules can be met.

As has already been described a small amount of water is evaporated from the product, normally less than 3%. This figure can be reduced by using a hydro vac facility which is supplied as standard equipment to our vacuum coolers. In some instances the removal of a small amount of water is an advantage in further reducing the deterioration of some types of fresh produce.

The main components of a Vacuum Cooler
Product Chamber

The size of the product chamber has to be large enough to hold the batch quantity for each cycle together with a working clearance to allow for badly stacked pallets or a possible future change in stack dimensions. We offer a range of chambers accomodating single or twin track conveyor systems. Any combination of batch quantity and pallet size can be designed into our system. The chamber doors can be hinged, sliding or vertical lift in manual or automatic options.

Vacuum Pump

This is used for the initial pump down of the vessel from atmospheric pressure to the flash point of water, at 20c that would be 23mb of vacuum. After reaching the flash point the efficiency of the pump is restricted by the size of the refrigeration plant. In general we would size the vacuum pump to reach flash point in 5-8minutes, the type of pump normally used being of the oil sealed sliding vane design.

Refrigeration Plant

Once the pressure reaches flash point water starts to evaporate from the surface of the product. It is this evaporation that achieves the cooling. In a machine that cools, say, 1000kg of product per cycle then 1860 m3 of vapour would be created and would need to be pumped from the chamber. In practice that is far too large for the vacuum pump to handle so a refrigerated coil block is fitted inside the chamber to recondense the vapour back into water - the refrigeration plant in effect acts like a vacuum pump. It is the size of the refrigeration plant that has a significant effect on the cooling cycle time. Generally we will quote on a cycle time of 25 minutes although we can achieve cycle times as low as 15 minutes.

Conveyor Systems

These play a significant part in cycle times, particularly with larger capacity vacuum coolers. To achieve rapid turnaround times we offer a variety of systems of manual or power assisted varients. We are able to offer a variety of solutions to suit any product handling enquiry.

Control System

The control system fitted is sophisticated rather than complicated and requires the operator to press only one button to start the cooling; the cycle stops automatically on reaching the pre-set temperature. PLC systems can be fitted to allow for cycle logging features etc. Whatever the chosen mode of operation, a fail-safe circuit ensures that if a fault is detected by any of the monitoring devices the system will be shut down in a safe condition.

The quality of practically all food products begins to deteriorate upon harvesting and continues to decline thereafter. The major effect in vegetable and plant harvesting, handling, processing and transportation is directed toward the maintenance of as much of the initial quality as possible. In the case of vegetables quality is aresult of physiological and microbiological activity in the harvested product. This deterioration is a function of time and temperature; in simple terms the faster it is cooled after harvesting the better the quality and the longer the shelf life.

Vacuum Cooling is the means to achieve this.